Electron diffraction demonstration apparatus

A description is given of apparatus specially designed for the Paris International Exhibition of 1937 in which it was desired that the diffraction of electrons could be shown to the public in such a way that a minimum of adjustment was necessary, that the public could operate the apparatus and that the possibilities of incorrect operation could be avoided. These conditions are fulfilled in a permanently evacuated tube which is described in detail. The diffraction of a 45kV electron beam by W foil 0.04 to 0.05 mu thick could readily be made visible to an audience.